The present invention relates to an implant for the connection of bones and in particular to a spinal column implant for the fusion of vertebral bones which is introduced between two vertebral bones to be fused.
Through the degeneration of the vertebral disc, in particular of the vertebral disc nucleus (nucleus pulposus) a loss of height in the affected vertebral disc space often comes about which is connected with a loosening of the vertebral disc annulus (annulus fibrosus) and of the ligaments. Through this the spinal column becomes instable at this location. The result is a horizontal displaceability of the vertebral bodies relative to one another (spondylolisthesis), which leads to impairments of the nerve roots in this region and/or of the spinal cord together with the pain resulting from this.
The principle for treating these symptoms consists in the operative excavation of the vertebral disc nucleus and the laying in or insertion respectively of onexe2x80x94in the region of the cervical vertebral columnxe2x80x94or of twoxe2x80x94in the region of the lumbar vertebral columnxe2x80x94sufficiently stable bodies in order to restore the normal height of the vertebral disc space. At the same time the horizontal displaceability must be prevented. This takes place either through the implant itself or through additional metal implants. These implants are subject in particular in the lumbar vertebral column to consideable forces, which can lead to the breakage of the metal implant. Therefore an attempt is made to have the intermediate vertebral insert grow together or fuse respectively as rapidly and as solidly as possible with the adjacent vertebral bodies.
A known possibility of fuhsing two vertebrae consists in the insertion of a suitably shaped cylinder or dowel into a prepared cavity which reaches the two vertebrae to be fused. The material which is required for this is removed beforehand from the patient for example from the pelvic ridge. From the thus won autogenic bone matter, that is, bone matter stemming from the same patient, an implant is produced and then inserted into the intervertebral space of the patient between the two vertebrae to be fused (auto-grafting).
The object of the present invention therefore consists in creating an implant for the fusion of bones which restores the correct distance between the vertebral bodies and the stabilty of the spinal column, which provokes no immune reactions and which accelerates the healing process.
This object is satisfied by a spinal column implant with the features of claim 1.
A particular advantage of the spinal column implant in accordance with the invention is given through the material used, which, as a result of its biological origin does not represent a foreign body. Through this the implant, which is produced of bone matter, contributes in its entirety, that is, the support element of for example cortical bone matter as well as the base body of spongeous bone matter, to the fusion of the vertebral bodies in that it converts into the body""s own tissue during the healing in.
Since the base body has no outer shell of hard bone matter, but rather consists of spongeous bone, the spongeous bone matter of the base body comes into direct contact with the bone surfaces of the vertebral bodies in order to form a bony connection with the latter and thereby to fuse them or to connect them to one another respectively.
The inventors have recognized that it is particularly advantageous to form the base body of spongeous, that is, relatively porous, bone matter in order to accelerate the healing in process. In order to be able however to take up the not inconsiderable forces which can arise between two vertebral bodies which are to be fused with one another, in accordance with the invention at least one load-carrying support element is embedded in the base body of spongeous bone matter which extends from one side to an oppositely lying side of the base body. The support element thus serves as a load-carrying part, in contrast to which the base body substantially has the function of seating the support element and enabling the growing together process with the surrounding bone matter.
In the description, the drawings and the subordinate claims, further advantageous embodiments of the spinal column implant in accordance with the present invention are set forth.
In accordance with a first advantageous embodiment the at least one support element consists of compact or of cortical bone respectively. Through this it is ensured on the one hand that high forces can be taken up by the spinal column implant. On the other hand the implant has no artifacts, which further accelerates the healing in process.
The support element can preferably be formed in the manner of a pin or a column respectively, with it also being possible for a plurality of support elements to be embedded in parallel into the base body. Depending on the stress distribution the support elements can also have different cross-sections in this situation.
In accordance with a further embodiment of the invention the support element is designed to be areal or wall-like, through which yet higher stresses on the implant are possible. In this it is advantageous when a plurality of areal support elements, the planes of which intersect, are embedded in the base body.
The support element or support elements can terminate at the outer contour of the base body or project beyond the outer contour of the base body in order to facilitate the fitting in of the implant between two vertebrae to be fused.
In accordance with a further embodiment of the invention the base body can contain at least one cavity which is accessible from its outer side for the reception of bone powder or bone granulate. The introduction of materials of this kind into a cavity of this kind improves the healing in process yet further.
In order to facilitate an integration of the base body between two vertebrae to be fused, the base body can furthermore have a surface which is corrugated, toothed or provided with knobs. Furthermore, the outer shape of the base body can also vary. The latter can be formed in the shape of a block, a rectangular parallelepiped or a wedge, with it being possible for rounded off corner contours or curved base bodies to be advantageous.
The implant is preferably matched in its size to the intervertebral space which is present between the adjacent vertebrae after the excavation of the intervertebral body. The application of the spinal column implant in accordance with the invention takes place after excavation of the vertebral disc with subsequent exposure of the vertebral bodies lying above and below it without it being necessary to damage healthy bone matter for this. This brings about the advantage that the existing intervertebral space is not enlarged and the supporting structures remain intact.
In accordance with the invention a suitable allogenic or xenogenic bone matter is processed in such a manner that it is preserved, is capable of storage and can be used in accordance with its purpose. The preservation of the bone matter can for example take place by means of freeze drying. The spongeous bone matter is preferably produced through solvent dehydration of native bone matter by means of an organic solvent which is miscible with water, e.g. methanol, ethanol, propanol, isopropanol, acetone, methyl ethyl ketone or mixtures of these solvents. The preservation and sterilization of the bone matter in accordance with this method is also a subject matter of the patent DE 29 06 650, the contents of which are taken up into the disclosure of the present application through this reference.
This method serves for the production of transplant preserves and enables a dehydration and exposure right into the fine structure of the fibrils of the bone matter, so that the processed bone matter has a morphological structure in a histological view which is very similar to that of the natural bone, and thus the desired properties of the bone matter are retained. This method of solvent dehydration also has the advantage that a substantially lower apparative cost and complexity is required in comparison with freeze drying.
Furthermore, the spongeous bone matter can also be produced through solvent dehydration of bone matter with the subsequent terminal sterilization, in particular through irradiation with gamma rays. Alternatively, the spongeous bone matter can be produced through aseptic processing of bone matter without terminal sterilization.